Insertion, or coordination, polymerization is a well-known chemical reaction sequence for preparing polymers and copolymers of ethylene, .alpha.-olefins, non-conjugated diolefins and strained ring cyclic olefins. And, in particular, coordination polymerization with monocyclopentadienyl metallocene catalyst systems is now well-known. Traditional Ziegler monomers, e.g., ethylene and .alpha.-olefins, such as propylene, 1-butene, 1-hexene, and 1-octene, are readily polymerized in the presence of Group 4 transition metals having as ligands one .eta.-5 bound cydopentadienyl ligand and three .sigma.-bound monoanionic ligands, preferably where one of the monoanionic ligands comprises a heteroatom that is covalently bound both to the Group 4 metal center and, through a bridging group, to a ring carbon atom of the cydopentadienyl ligand group.
Geminally disubstituted olefin monomers, such as isobutylene, are known not to be readily polymerizable by insertion, or coordination, mechanisms. In the chapter on "Insertion Polymerization", Encycl. of Polm. Sci. and Eng., vol. 8, p. 175 (Wiley Interscience, 1988), the statement is made that ". . . 1,1-disubstituted .alpha.-olefins are neither homo- nor copolymerized with other monoolefins." Instead such disubstituted .alpha.olefins are typically polymerized and copolymerized by cationic or carbocationic polymerization with Lewis acid catalyst systems known to initiate the formation of carbocations. However, since ethylene is not readily polymerized by cationic techniques, see Kennedy, J. P., Carbocationic Polymerization of Olefins: A Critical Inventory, p. 53 et seq. (John Wiley & Sons, 1975), ethylene copolymers with disubstituted .alpha.-olefns are largely unknown.
In Kennedy and Johnston, Isomerization Polymerization of 3-Methyl-1-butene and 4-Methyl-1-pentene, Advances in Polymer Science, p. 58-95 (1975), it was stated to be of interest to examine the cationic isomerization polymerization of 4-methyl-1-pentene because the completely isomerized structure can be viewed as a perfectly alternating copolymer ethylene and isobutylene. A structure which, in the reporters' words, "cannot be synthesized by conventional techniques", page 61. Due to multiple isomerization reactions occurring under the cationic isomerization polymerization reactions the sought alternating ethylene-isobutylene was observed, in amounts only up to 55 mol. % --(CH.sub.2 --CH.sub.2 --CH.sub.2 --C(CH.sub.3).sub.2)-- with the remainder consisting of the 1,2 addition product --(CH.sub.2 CH(CH.sub.2 CH(CH.sub.3).sub.2))-- and the 1,3 addition product --(CH.sub.2 CH.sub.2 CH(CH(CH.sub.3).sub.2)--. The 1,3-addition product is only possible using the cationic chemistries disclosed in the reference and is incompatible with insertion polymerization.
The use of both biscyclopentadienyl and monocyclopentadienyl metallocene catalyst systems for combined carbocationic and coordination polymerization of mixed feeds of ethylene and isobutylene at temperatures below 20.degree. C. is described in WO 95/29940. Copolymerization of ethylene and isobutylene is said to be enabled by use of the described catalyst systems, in particular, sequential feeding of each monomer is said to enable blocky copolymers of polyisobutylene-co-polyethylene. Example E describes ethylene/isobutylene copolymerization concurrent with the homopolymerization of both the isobutylene and the ethylene at -20.degree. C. with bis-(cyclopentadienyl)hafnium dimethyl and bis-(pentamethylcyclopentadienyl)-zirconium dimethyl, both activated by triphenylmethyl-tetrakis(perfluorophenyl)boron. The amount produced of ethylene-isobutylene copolymer was less than 1.3 weight % of the total polymer products. Copolymerization of 2-methylpropene (isobutylene) and ethylene at 30.degree. C. and 50.degree. C. with ethylene-bis(indenyl)zirconium dichloride when activated with methylalumoxane was reported in "Isotactic Polymerization of Olefins with Homogeneous Zirconium Catalysts", W. Kaminsky, et al, Transition Metals and Organometallics as Catalysts for Olefin Polymerization, page 291, 296 (Springer-Verlag, 1988). Incorporation of isobutylene was reported to be less than 2.8 mol. %, the only example illustrates 1.35 mol. %.
In view of the above, additional means of manufacturing polyolefins, particularly a means of incorporating geminally disubstituted .alpha.-olefins in such polyolefins is highly desirable. Copolymer compositions comprising ethylene and geminally disubstituted olefins, optionally with other polymerizable olefinically-unsaturated monomers, would provide new compositions useful in many applications and would serve the function of economically utilizing the inherent feedstock make-up in petroleum refining processes.